1. Field of the Invention
The present invention relates to an exhaust gas recovery method and apparatus. In particular, the present invention relates to an exhaust gas recovery and reuse method and apparatus, in which a volatile organic compound, such as a solvent, in the exhaust gas is recovered and reused.
2. Description of the Related Art
A volatile organic compound gas, such as a solvent, is generated from a factory. It is preferable that the gas is recovered and reused. Various methods of recovering the solvent and the like are proposed. Absorbing a volatile organic compound by an adsorbent such as active carbon is generally known as a conventional method of recovering a volatile organic compound exhausted from a factory or the like. However, in this method, because some types of volatile organic compounds, for example, solvent gases, cannot be adsorbed by an adsorbent, they are released into the atmosphere. Namely, with respect to the some kinds of the volatile organic compounds, the adsorbent does not have removal ability. Also, there are cases in which, with respect to some types of volatile organic compounds, the deterioration rate of the active carbon is high. In such cases, a problem arises in that the cost for replacing the active carbon (running cost) becomes high.
Recovering the volatile organic compound gas by a scrubber is another generally known method. However, in a case where the volume of gas is large and the concentration of the volatile organic compound gas is small, a large amount of water for the scrubber is needed. In this case, because the amount of water for the scrubber is large, a large amount of waste water, which includes the volatile organic compound recovered from the scrubber, is generated. Therefore, many processes, in which the waste water is processed so as to recover the volatile organic compound therefrom, are needed. Accordingly, this method is not economical.
The present invention takes the facts mentioned above into consideration, and an object of the present invention is to provide an exhaust gas recovery method and apparatus therefor, in which a volatile organic compound, such as a solvent, in a large amount of exhaust gas, can be recovered efficiently and at a relatively low cost, and the recovered volatile organic compound can be reused.
Exhaust gas recovery methods of the present invention are:
(1) An exhaust gas recovery method comprising: a first process in which a volatile organic compound gas is absorbed by water; a second process in which water including the volatile organic compound, which is obtained in the first process, is frozen and concentrated such that the water including the volatile organic compound, which is obtained in the first process, is separated into water including a high concentration of the volatile organic compound, level of concentration being higher than that of the water including the volatile organic compound which is obtained in the first process, and ice; a third process in which cold of the ice obtained in the second process is used; and a fourth process in which the water including a high concentration of the volatile organic compound, which is obtained in the second process, is reused.
(2) An exhaust gas recovery method, according to (1), wherein the fourth process is a process in which the water including a high concentration of the volatile organic compound, which is obtained in the second process, is separated into the volatile organic compound; and water.
(3) An exhaust gas recovery method according to (2), further comprising: a fifth process in which the separated water obtained in the fourth process is supplied to the first process.
(4) An exhaust gas recovery method according to (2) or (3), further comprising: a sixth process in which the separated volatile organic compound obtained in the fourth process is supplied to a facility where the volatile organic compound is needed.
(5) An exhaust gas recovery method according to (1), (2), (3) or (4), further comprising: a seventh process in which water, which is generated due to the cold of the ice being used in the third process, is supplied to the first process.
(6) An exhaust gas recovery method according to (1), (2), (3), (4) or (5), wherein the volatile organic compound is an organic solvent.
(7) An exhaust gas recovery method, according to (1), (2), (3), (4), (5) or (6), wherein the volatile organic compound included in the water, which is generated due to the cold of the ice being used in the third process, is decomposed in a waste water processing facility.
In an exhaust gas recovery method of the present invention, in the first process, a volatile organic compound gas is absorbed by water. In the second process, when the water including the volatile organic compound, which is obtained from the first process, is frozen, the water becomes an ice composed of substantially pure water. In contrast, the volatile organic compound does not freeze, and is in a state of being dissolved in water. Accordingly, the concentration of the volatile organic compound in the water which is subjected to the second process becomes high. This water including the volatile organic compound in a high concentration is separated into water and the volatile organic compound in the fourth process. In the fourth process, because the concentration of the volatile organic compound in the water is high, the amount of the water which is subjected to this separating process is small, therefore, a low level of energy is needed for this separating process.
Exhaust gas recovery apparatuses of the present invention are:
(8) An exhaust gas recovery apparatus comprising: a first section in which a volatile organic compound gas is absorbed by water; a second section in which water including the volatile organic compound, which is obtained in the first section, is frozen and concentrated such that the water including the volatile organic compound, which is obtained in the first section, is separated into water including a high concentration of the volatile organic compound, level of concentration being higher than that of the water including the volatile organic compound which is obtained in the first section, and ice; a third section in which cold of the ice obtained in the second section is used; and a fourth section in which the water including a high concentration of the volatile organic compound, which is obtained in the second section, is reused.
(9) An exhaust gas recovery apparatus according to (8), wherein the first section is a scrubber.
(10) An exhaust gas recovery apparatus according to (8) or (9), wherein the fourth section is a distiller.
The exhaust gas recovery is preferably implemented by the exhaust gas recovery apparatus of the present invention. In particular, in a scrubber, the contact efficiency rate of the water drops or the water film contacting the volatile organic compound gas is high. Also, in a distiller device, the water and the volatile organic compound are separated efficiently, by use of the difference between the boiling point of water and the boiling point of the solvent.